Commit 3592806c authored Dec 12, 2013 by Kirill A. Shutemov Committed by Linus Torvalds Dec 12, 2013

thp: move preallocated PTE page table on move_huge_pmd()



Andrey Wagin reported crash on VM_BUG_ON() in pgtable_pmd_page_dtor() with
fallowing backtrace:

  free_pgd_range+0x2bf/0x410
  free_pgtables+0xce/0x120
  unmap_region+0xe0/0x120
  do_munmap+0x249/0x360
  move_vma+0x144/0x270
  SyS_mremap+0x3b9/0x510
  system_call_fastpath+0x16/0x1b

The crash can be reproduce with this test case:

  #define _GNU_SOURCE
  #include <sys/mman.h>
  #include <stdio.h>
  #include <unistd.h>

  #define MB (1024 * 1024UL)
  #define GB (1024 * MB)

  int main(int argc, char **argv)
  {
	char *p;
	int i;

	p = mmap((void *) GB, 10 * MB, PROT_READ | PROT_WRITE,
			MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
	for (i = 0; i < 10 * MB; i += 4096)
		p[i] = 1;
	mremap(p, 10 * MB, 10 * MB, MREMAP_FIXED | MREMAP_MAYMOVE, 2 * GB);
	return 0;
  }

Due to split PMD lock, we now store preallocated PTE tables for THP
pages per-PMD table.  It means we need to move them to other PMD table
if huge PMD moved there.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Andrey Vagin <avagin@openvz.org>
Tested-by: Andrey Vagin <avagin@openvz.org>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3e1e4a5f

mm/huge_memory.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -1481,8 +1481,18 @@ int move_huge_pmd(struct vm_area_struct vma, struct vm_area_struct new_vma,
		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
		VM_BUG_ON(!pmd_none(*new_pmd));
		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
		if (new_ptl != old_ptl)
		if (new_ptl != old_ptl) {
		pgtable_t pgtable;

		/*
		* Move preallocated PTE page table if new_pmd is on
		* different PMD page table.
		*/
		pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
		pgtable_trans_huge_deposit(mm, new_pmd, pgtable);

		spin_unlock(new_ptl);
		}
		spin_unlock(old_ptl);
		}
		out:

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